FIG. 17 is a schematic for explaining a rotor blade and a stationary blade showing a blade structure of a conventional gas turbine. FIG. 18 is a sectional view cut along the line D-D of FIG. 17. FIG. 19 is a perspective view of the stationary blade and the rotor blade shown in FIG. 18. A blade structure of a conventional gas turbine includes a plurality of stages of stationary blades 81 arranged annularly on a casing 61 and a plurality of stages of rotor blades 71 arranged annularly on a rotor 65 that is rotatable about a rotating axis 66. The stationary blades 81 and the rotor blades 71 are arranged alternately in the direction of the rotating axis 66. In some gas turbines having such a blade structure, a shroud (not shown) is not provided on each rotor blade 71 on a side of a tip portion 72 located on a side of an outer edge portion of the rotor blade 71 in the radial direction of the rotor 65. More specifically, shrouds are typically not provided particularly on high-pressure stages of the rotor blades 71. In such cases, a gap is provided between the tip portion 72 of each rotor blade 71 and an end wall 62 of the casing 61. That is, a tip clearance 90 is provided therebetween. Thus, when the tip clearance 90 is provided therebetween, sometimes combustion gas leaks from the tip clearance 90 and flows downstream when the rotor 65 rotates. As a result, the pressure loss of the gas turbine may increase.
When the rotor 65 rotates, a main flow 92 of the combustion gas flows along the shape of a back surface 74 and a ventral surface 75 of each rotor blade 71, and flows into the stationary blade 81 located downstream of the rotor blade 71. Thus, when combustion gas flows into each stationary blade 81, the combustion gas flows generally along the shape of a back surface 84 and a ventral surface 85 near a leading edge 86 of the stationary blade 81. On the other hand, a leakage flow 93 of combustion gas that flows leaking from the tip clearance 90 flows into the stationary blade 81 at an angle different from the angle at which the main flow 92 of combustion gas flows thereinto.
Thus, in the combustion gas flowing along each rotor blade 71, there is a difference between a pressure on the side of the back surface 74 thereof and a pressure on the side of the ventral surface 75 thereof, and the pressure on the side of the ventral surface 75 is higher than the pressure on the side of the back surface 74. Therefore, the combustion gas flowing on the side of the ventral surface 75 leaks from the tip clearance 90 and flows into the side of the back surface 74 as the leakage flow 93. The leakage flow 93 flows so that the leakage flow 93 and the main flow 92 of combustion gas cross each other. Thus, when the leakage flow 93 flows into the stationary blade 81, the leakage flow 93 flows thereinto at an angle different from the angle at which the main flow 92 of combustion gas flows thereinto. Because the leakage flow 93 does not flow in the direction along the shape of the stationary blade 81, the pressure loss increases.
Therefore, some blade structures of conventional gas turbines are designed to reduce the pressure loss due to combustion gas leaking from the tip clearance 90. For example, in a blade structure of a gas turbine disclosed in Japanese Patent Application Laid-open No. 2002-213206, each stationary blade is so designed that a leading edge including an angle, that is, an angle between the back surface and the ventral surface near the leading edge of the stationary blade at the tip portion, is different from a leading edge including an angle at any position other than the tip portion. More specifically, the leading edge including an angle at the tip portion is larger than a leading edge including an angle at any position other than the tip portion. Thus, relationship between an incidence angle, that is, an angle between the direction in which the stationary blade is formed and the direction in which the combustion gas leaking from the tip clearance flows, and the pressure loss fluctuates less. Therefore, the pressure loss due to combustion gas leaking from the tip clearance of the rotor blade can be reduced.